Broadly cross-resistant clones of mouse neuroblastoma isolated with adriamycin maytansine, vincristine or Bakers antifol were 2-100 fold collaterally hypersensitive to 6-mercaptopurine (6MP), 5-fluordeoxyuridine (5-FUdR), 2-deoxyglucose and 5-bromodeoxyuridine. Clones resistant to 6MP or FUdR were hypersensitive to the other 3 phosphorylatable drugs. All clones demonstrate 12-270 fold increased levels of alkaline phosphatase (AP) and/or alkaline phosphodiesterase (APD) proteins. AP increases are inversely proportional to those of APD as measured by immunoprecipitation. Double-minute chromosomes and 16-20 day resistance half-lives upon further growth without selective drugs suggest gene amplification. Preliminary data indicate that 6MP and 5-FUdR markedly prolong the survival of syngeneic mice inoculated with a Bakers antifol-selected cross-resistant clone but not wild-type neuroblastoma. Uptake of 6MP was normal in all collaterally hypersensitive mutants. High AP or APD levels, possibly the result of gene amplification mediated inductions, correlate with collateral sensitivity to the 4 phosphorylatable drugs. Furthermore, tetramisole or db-cAMP, inhibiting or increasing AP, respectively, markedly reduced or increased the respective collateral sensitivity of Bakers antifol selected cells to 6MP. Both elevated phosphatases may increase the toxicity of FUdR and 6MP by interfering with de novo and salvage pathways to nucleotide synthesis, or by altering normal and drug nucleotide pools, further inhibiting cell division. We propose to determine optimal conditions for this collateral sensitivity with additional drugs and phosphatase inducers, to analyze the mechanism of phosphatase protein increases, to analyze the causality of increased AP and APD in this collateral sensitivity by examining the effect of APD inhibitors, quantitating the flux, pool size and incorporation of phosphorylated drug and normal nucleotide metabolites and 5-phosphyribosyl-1-pyrophosphate and examining the relative activities of induced phosphatases toward these metabolites, to assess phosphorylatable drug chemotherapy of additional high AP and APD drug resistant and revertant clones in cell culture and in Ajaz mice, and to extend these phosphatase and collateral sensitivity assays to analogous drug-resistant human neuroblastoma and other cancer cell lines. This will assess the breadth of applicability and the validity of phosphatase markers in directing collateral chemotherapy of drug resistant cancers.